The use of parabolic aluminized reflector (PAR), elliptical reflector (ER), or reflector (R) lamps for general spot, downlighting, and/or flood lighting applications is well established. In particular, R, PAR, and ER type lamps have been accepted as the lamps of choice for short to medium distance outdoor uses, as well as for indoor display, decoration, accent, and inspection applications of down lighting.
Traditionally, incandescent PAR-type lamps, for example the PAR38, have used a filament mounted transversely in the reflector, that is, perpendicular to its axis of symmetry. Although not the best orientation for optical considerations, this was the simplest configuration to manufacture.
The optics of this configuration result in an asymmetric beam pattern and the spreading of stray light outside of the useful beam. Additionally, it was necessary to hermetically seal the outer jacket of these lamps to maintain the proper atmosphere for filament operation. This was accomplished by flame-sealing the reflector and lens.
With the introduction of PAR lamps using a halogen capsule as a light source, came lamps with axially mounted filaments yielding a more symmetric beam pattern and more efficient collection of light by the reflector into a useful beam.
Part of this gain in optical efficiency is due to the fact that the these lamps use a compact filament which more nearly approaches the theoretically ideal "point" source.
In Capsylite lamps operating at 120-130 AC; 60 Hertz such compact filaments are in part made possible by the use of a halfwave rectifying diode which reduces the effective capsule voltage from 120V to about 84V. Furthermore, with a hermetically sealed capsule, the atmosphere in the outer envelope is no longer critical, and lamps with non hermetically sealed outer jackets have become feasible.
In European line voltage PAR lamps, typically of 220 to 250V, halogen capsules have not been used because of the exceedingly long and fine filament wire that is required at this high voltage.
Low wattage (&lt;150W), line voltage filaments tend to be long and flimsy, prone to sag and requiring multiple supports which reduce efficiency. Voltage reducing diodes cannot practically be used because they produce objectionable flickering of the filament when run on the 50 cycle AC which is standard in Europe.